Light received through the eye regulates an array of non-image forming photoresponses, including entrainment of the circadian clock to the ambient light dark cycle, light modulation of alertness/sleep, light suppression of pinel melatonin synthesis and release, and acute regulation of transcription in adrenal galnds. By classical genetics and cell biological studies we have determined an opsin class of GPCR, called melanopsin is the dominant photopigment that mediate these non-image forming responses. Melanopsin is expressed in a small subset of retinal ganglion cells. Unlike the classical vertebrate rod/cone photopigments, melanopsin uses a different mechanism for regeneration of its photopigment and a distinct signaling mechanism to transduce the light information. This has opened up potential to develop pharmacological agents to specifically modulate melanopsin function. Although photosensitive opsins are the founding members of GPCRs, no HTS compatible assay for this class currently exists. In this proposal we plan to generate cell lines stably expressing melanopsin and beta arrestin each bearing specific tags, such that photoactivation of melanopsin leads to a luminescent readout. We plan to use this cell line to develop a high through-put screening (HTS) compatible assay to monitor photoactivation of melanopsin. The assay will be optimized and miniaturized to be run in 384-well format, and the optimized assay will be used to screen a small library of compounds. Successful completion of the experiments will generate a novel HTS compatible assay for an opsin class of photopigment and a few potential modulators of an opsin class of photopigment. Ultimately, small molecule modulators of melanopsin will offer valuable tools to interrogate the role of melanopsin in non-image forming photoresponses in non-model organisms. PUBLIC HEALTH RELEVANCE: We have established a critical role of a novel light receptor melanopsin in adjusting our biological clock and sleep-wake rhythms to the day: night cycle. The goal of this research proposal is to develop a method to reliably measure melanopsin function. This method would then be used to screen a large number of potential drug compounds to find ones that can mimic light or darkness and can be ultimately used to treat diseases like depression, various sleep disorders and jet-lag.